Alzheimer's disease is the most common age-related neurodegenerative disorder. It has been widely accepted that abnormal production or accumulation of amyloidogenic peptides (Abeta), derived from sequential processing of amyloid precursor protein (APP) by beta-secretase and gamma-secretase, is tightly linked to AD pathogenesis. Our main research objectives will be focused on the regulated APP processing and production of (Abeta) in cells. A type I transmembrane aspartyl protease have been recently identified as beta-secretase, or called BACE1. We believe that all physiological functions are well balanced by various negative and positive modifiers. It is conceivable that BACE1 activity in cells is also modulated by natural factors and a shift of the modulating balance will clearly affect Abeta production. We hypothesize that abnormal fluctuations of BACE1 modifiers in human brains contribute to the amyloid depositions and the subsequent AD pathogenesis. Recently, we found that reticulon 3 (RTN3) clearly modulates BACE1 activity. RTN3 is one of the members of RTN family that comprises four members and all the members share highly conserved C-terminal Reticulon Homology Domain (RHD). Our specific objectives in this proposal are to delineate the molecular mechanism in which RTN3, and probably its family members, negatively modulate BACE1 activity and to explore potential applications of reticulon proteins in Alzheimer's therapeutics. Vigorous biochemical, molecular cell biology approaches combined with genetic methods will be used to address the following Specific Aims. Aim 1 -To investigate interactions of BACE1 with RTN family members. Aim 2 - To explore the mechanism by which BACE1 activity is modified by RTN3. Aim 3 To validate RTN3 as a negative BACE1 modifier in vivo. We believe that results from this study will provide valuable insights into the molecular mechanisms of RTN3 and its family members in negatively modulating BACE1 activity.